Chloropentafluoroethane, which is used as a solvent, propellant or refrigerant fluid, is prepared by known processes, for example from perchloroethylene, chlorine and hydrofluoric acid (East German Pat. No. 117,580) or by a gas phase reaction of trichlorotrifluoroethane C.sub.2 F.sub.3 Cl.sub.3 with hydrofluoric acid in the presence of aluminium trifluoride (Japanese Publication No. 48-26,729/73).
U.S. Pat. No. 3,087,974 describes the vapor phase disproportionation of chlorofluoro compounds on a catalyst without the addition of hydrofluoric acid. The disproportionation of dichlorotetrafluoroethane takes place according to the reaction: EQU 2C.sub.2 Cl.sub.2 F.sub.4 .fwdarw.C.sub.2 ClF.sub.5 +C.sub.2 Cl.sub.3 F.sub.3
This catalyst is activated alumina of high surface area which is treated with a fluorocarbon compound before being used for the disproportionation reaction. The conversion of CF.sub.2 ClCF.sub.2 Cl to C.sub.2 ClF.sub.5 does not exceed 34% on a molar basis and a high proportion of C.sub.2 Cl.sub.3 F.sub.3 is produced as a by-product.
U.S. Pat. No. 3,258,500 describes a vapour phase catalysed fluorination using hydrofluoric acid. The dichlorotetrafluoroethane (CF.sub.2 Cl--CF.sub.2 Cl) and hydrofluoric acid (HF), in a molar ratio [HF/CF.sub.2 Cl--CF.sub.2 Cl] of between 4 and 5, react at 400.degree. C. on a chromium oxide catalyst. The proportion of hexafluoroethane C.sub.2 F.sub.6 formed is 0.19 on a molar basis relative to C.sub.2 F.sub.5 Cl.
A paper by L. Marangoni et al., "Preparation of chloropentafluoroethane from dichlorotetrafluoroethane" (Journal of Fluorine Chemistry 19, 1981/82, pages 21 to 34) also describes a chromium oxide-based catalyst for the gas phase manufacture of C.sub.2 F.sub.5 Cl from C.sub.2 F.sub.4 Cl.sub.2 and HF. The degree of conversion of C.sub.2 Cl.sub.2 F.sub.4 is between 72 and 75%, the yield of C.sub.2 F.sub.5 Cl is between 89 and 92%, but the formation of hexafluoroethane is still 8% on a molar basis of the formation of C.sub.2 F.sub.5 Cl.
A paper by M. Vecchio et al., "Studies on a vapor-phase process for the manufacture of chlorofluoro-ethanes" (Journal of Fluorine Chemistry, 4, 1974, pages 111 to 139) describes the same reaction as the preceding paper but on a catalyst based on aluminium fluoride doped with nickel, iron and chromium halides. The degree of conversion of C.sub.2 F.sub.4 Cl.sub.2 does not exceed 41% and the molar pourcentage of C.sub.2 F.sub.5 Cl at the reactor outlet is 38%.
The catalysts of the prior art are difficult to prepare, while the yields and selectivities for C.sub.2 F.sub.5 Cl are mediocre.
The present invention overcomes all these disadvantages by offering a simple, flexible and economical process for producing C.sub.2 F.sub.5 Cl.